Interference occurs when unwanted radio frequency signals disrupt the use of automobile's radio system. Interference may prevent reception altogether, may cause only a temporary loss of a signal, or may affect the quality of the sound. The interference in automobile radios comes from a variety of sources. The most common sources for interference are electric and electronic systems in an automobile. One probable cause of this type of interference is the cars spark plug wires which degrade over time. Another source of interference can be the charging system of your car. The alternator which produces electricity to charge your cars battery is essentially a source of electro-magnetic energy.